This invention relates to a temperature controlled high voltage regulator for count rate compensation of radiation detectors. The United States Government has rights to this invention pursuant to Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC, awarded by the U.S. Department of Energy.
Radiation contamination technicians are often required to monitor for contamination in areas where temperature is uncontrolled. In order to perform this task, sensitive instrumentation is commonly used that incorporates gas flow proportional radiation detectors. This type of detector is used due to its excellent sensitivity to beta and alpha radiation and relative insensitivity to gamma radiation.
Unfortunately, these detectors are very susceptible to changes in temperature. As the temperature increases, the sensitivity increases; as the temperature decreases, the sensitivity decreases, relative to the original calibration temperature. This susceptibility can increase or decrease sensitivity resulting in radioactive contamination levels being mis-stated, missed entirely, or overstated, thus causing improper corrective actions to be taken.
Any change in ambient temperature causes immediate effects to the sensitivity of the detector due to changes that occur in the flow gas that is used. The typical gas used in the United States is P-10 (90% argon and 10% methane). Although changing gas pressure should work, this method is not possible due to detector design.
U.S. Pat. No. 3,505,583 to Burkhardt shows a high voltage regulator for providing a constant reference voltage to reactive loads such as RC timing circuits used in bomb fuses and other ordnance devices. Burkhardt""s invention, however, is limited in scope to RC timing circuits and limited in purpose to the timing accuracy in ordnance devices and does not address the effect of temperature.
U.S. Pat. No. 3,126,508 to Eriksson shows a temperature dependent control of the output voltage of an energy source which is specially suitable for bridge networks. Eriksson""s invention, however focuses on providing output voltage for stabilizing the bridge function.
U.S. Pat. No. 3,701,004 to Tuccinardi shows a circuit for producing a repeatable predetermined voltage as a function of temperature and including a component having a known temperature coefficient characteristic. Tuccinardi""s invention, however, specifically states that the regulator discussed therein refers not to a constant voltage circuit, but instead to a circuit capable of a predetermined output voltage which varies in accordance with temperature.
Accordingly, a need in the art exists for a temperature controlled high voltage regulator for count rate compensation of radiation detectors which will reduce or eliminate the susceptibility of the detectors to changing temperature.
In view of the above need, it is an object of this invention to provide an apparatus that is capable of automatically adjusting the applied high voltage based upon the ambient temperature.
It is an object of this invention to provide an apparatus as in the above object that constantly senses temperature changes and adjusts high voltage to maintain a stable response reading in an attached radiation detector.
It is an object of this invention to provide an apparatus as in the above object that is easily interfaced with different radiation detectors.
It is an object of this invention to provide an apparatus as in the above object that is easily interfaced with different count rate meters.
It is an object of this invention to provide an apparatus as in the above object that has a silicon diode for the temperature sensor.
Briefly, the present invention is a temperature controlled high voltage regulator for count rate compensation of a radiation detector having an input voltage, an output voltage and a dc reference voltage. The regulator comprises a temperature sensor for measuring ambient air temperature; a sensing diode amplifier connected to the temperature sensor for providing a constant current through the temperature sensor; a dc voltage reference amplifier connected to the sensing diode amplifier for boosting the dc reference voltage; a temperature reference amplifier connected to the dc voltage reference amplifier for providing a temperature-proportional reference voltage for a connected error amplifier through the dc voltage reference amplifier, the connected error amplifier providing an amplified error signal for reading feedback voltage; a current controlled voltage attenuator connected to the error amplifier for regulating the output voltage to the attached radiation detector; a high voltage input and output sensor circuit, which includes two hi-Z input buffer amplifier for bufffering the sensor from loading effects and for adjusting any feedback voltage, connected to the current controlled voltage attenuator for measuring the input and output voltages; and a difference amplifier connected to the error amplifier for providing a ground referenced feedback voltage, connected in such manner so as to sense the variable temperature and adapt the input voltage such that the output voltage changes with temperature, permitting the radiation detector to perform at an enhanced level of accuracy, regardless of ambient temperature.
In one embodiment, the radiation detector is a gas flow proportional detector. In a preferred embodiment, the temperature sensor is comprised of a silicon diode, and the current controlled voltage attenuator is ground-referenced. The voltage reference amplifier is calibrated for boosting the dc reference voltage from about 200 milli-volts to about 760 milli-volts, and the current controlled voltage attenuator is isolated from the reference amplifier by a protective box so that calibration adjustments can be made safely.
Also provided is a method for controlling the high voltage to an attached radiation detector to enhance detection accuracy independent of ambient temperature, comprising the steps of: measuring ambient air temperature by using a temperature sensor; providing constant current through the temperature sensor by using a sensing diode amplifier; boosting a dc reference voltage by using a dc reference amplifier; providing a temperature-proportional reference voltage by using a temperature reference amplifier; regulating output voltage to the attached radiation detector by using a current controlled voltage attenuator; measuring input and output voltages by using a high voltage input and output sensor circuit which includes two hi-Z buffer amplifiers for buffering the sensor circuit from loading effects and for adjusting feedback voltage; reading feedback voltage by using an error amplifier to provide an amplified error signal; and providing a ground referenced feedback voltage to the error amplifier by using a difference amplifier so that the output voltage to the attached radiation detector changes with temperature, permitting the detector to perform at an enhanced level of accuracy, regardless of ambient temperature.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.